As disclosed, for example, in JP 9-98972 A, a conventional living body optical measuring device has a measuring probe attached to a subject and a device main body connected to the measuring probe. The measuring probe has an irradiation optical fiber for irradiating the subject with measurement light generated in the device main body, a detection optical fiber for receiving the measurement light transmitted through the subject, that is, a living body passing light, and guiding it to the device main body; a fixing member for securing the distal end portions of the irradiation and detection optical fibers at predetermined positions of the subject; and a fixation belt for securing the fixing member to the subject.
However, in the case, for example, of the measurement of a newborn baby or a measurement of long duration, it is necessary to perform, apart from a measurement in a seated position or a standing position, measurement in which the subject lies down, and there is demand for a measuring probe allowing such measurement. That is, there is demand for a measuring probe which can be attached to the subject without damaging the optical fibers even when the subject lies down.